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400
Democritus
400BC
atomic theory posited that all matter is made up small indestructible units he called atoms. -
Antoine Lavoisier
Antoine Lavoisier was never credited with the discovery of any element. -
John Dalton
proposed that elements consisted of atoms that were identical and had the same mass and that compounds were atoms from different elements combined together. -
James Maxwell
Calculating the speed of electromagnetic waves, Maxwell postulated that light is a form of electromagnetic radiation exerting pressure and carrying momentum. This provided the basis for Einstein's work on relativity from which the relationship between energy, mass and velocity contributed to the theory underlying the development of atomic energy. -
Erwin Schrodinger
Schrödinger's wave equation was based on the Heisenberg uncertainty principal that the position and velocity of a electron cannot be determined accurately (accuracy in one will sacrifice accuracy in another). Schrödinger's wave equation gave a wave function, which squared gave the probability cloud of electrons. Therefore, Schrödinger's contribution resulted in the electron cloud model of the atom. -
J.J. Thomson
J J Thomson was the first person to suggest the theory of the atom containing positive and negative particles, and demonstrated the latter which he called electrons. -
Ermst Rutherford
discovered alpha, beta, and gamma rays in radiation. -
Marie Sklodowska Curie
Many journals state that Curie was responsible for shifting scientific opinion from the idea that the atom was solid and indivisible to an understanding of subatomic particles. -
Max Planck
His work contributed significantly to the understanding of atomic and subatomic processes. Planck's work in thermodynamics led to the formulations of his quantum theory. -
Werner Heisenberg
Heisenberg worked out that particles had a lot more energy over short distances than expected. He realized that a particle can borrow energy as long as it is paid back in a short time. The relationship he came up with was the position and energy of a particle can only be known to a certain amount. (the certainty in position and the certainty in momentum is more or less equal to plank's constant). This is known as the uncertainty principle.
This is believed to be the way a particle escapes the c -
H.G.J. Moseley
discovered that the number of protons in an element determines its atomic number. -
Niels Bohr
proposed an atomic structure theory that stated the outer orbit of an atom could hold more electrons than the inner orbit. -
Robert Millikan
Robert Millikan won the 1923 Nobel Peace Prize for his oil drop experiment and his photoelectric effect experiment. Robert used his oil drop experiment to discover the electron's charge independently. -
James Chadwick
discovered neutrons, particles whose mass was close to that of a proton. -
Modern Theroy
Quantum theory has shown us that the electrons although they are particles also exhibit properties of waves. Now we think of the atom as a nucleus that is surrounded by probability clouds. The clouds represent the most probable locations of electrons. We still refer to these clouds as orbitals. -
Aristotle
322-384 BC
He claimed that there was no smallest part of matter and that different substances were made up of proportions of fire, air, earth, and water. As there were of course no experimental means available to test either view, Aristotle's prevailed mainly because people liked his philosophy better.
